There are two more guards to take out on the hilltop. One is crouched down and not moving at all, just north of the position of the last guy you downed. For now, go northwest a bit, passing behind the snipers to a cul-de-sac area. You can creep right up to the large rock that the PMC patrols by and wait for him to start moving eastward (to the right) before rolling around the left side of the rock and behind the soldier. You'll want to make sure the guy is behind the tallest part off the ledge behind him to stay out of the view of any enemies to the north.

From there you can easily sneak up behind the dude just crouched down to the east. Put him down to finish clearing the clifftop. Start moving north toward the cliff's edge and follow the eastern path that runs downhill along a fence. The militia should have taken position just east of the power station and are assaulting it from the side.

Crawl on your belly, continuing north, until you can stare into the northeast corner of the power station, an area with a couple of enemies behind an open fence. There's a route to the east from which militia forces will come, but they have difficulty infiltrating the base. While hidden on the ground, tranquilize the PMC soldiers in the northeast corner of the base. The militia will eventually push through the fence and start talking about disabling the power station.

If you hang out long enough, the militia will destroy the power station (signalled by a lot of electricity noise). Wait longer and they'll overrun the base, eliminating all enemies (signalled by them cheering). When the base is won by the militia, you can run inside to find myriad items. The best items are semi-hidden in the northwest corner of the base, which you can only get to with some creative maneuvering. Climb a ladder in the southwest corner of the base to the top of the power line structure. From the top of the northern ladder (while still hanging on it), you can sidle along the disabled power line, heading north to overhang a second power line structure. Drop down onto that structure and you can climb down the ladder to collect the items that litter this area, including a rifle scope and a FIM-92A surface-to-air missile.

When you're done collecting items, climb the boxes to the south and use a dive roll to hop back over the gate. Make your way to the road north of the power station to trigger a cut scene.